1. Field of Invention
The invention relates to a control system for automatically starting an internal combustion engine, for example, a gasoline engine, a diesel engine and the like. More specifically, the invention relates to a control system for an internal combustion engine that is equipped with a starting mechanism, which is electrically powered to crank the internal combustion engine.
2. Description of Related Art
An economy-running control or eco-run control has been known to improve the fuel efficiency of a vehicle that is driven by an internal combustion engine. The eco-run control operates to stop an internal combustion engine of a vehicle when the vehicle is in a stopped state. The eco-run control automatically stops the internal combustion engine when it determines that the vehicle will not take off immediately after the vehicle is stopped, and re-starts the internal combustion engine when it determines that a request to start the vehicle has been issued.
The eco-run control for automatically stopping and re-starting the internal combustion engine is automatically performed, irrespective of the intention of a driver or a passenger, when a vehicle is in a temporary stopped state during the running of the vehicle. Therefore, it is preferable to keep the driver or the passenger of the vehicle from sensing the stopping and re-starting of the internal combustion engine of the vehicle. When the vehicle does not timely start upon the driver's operation to cause the vehicle to take off and instead starts after a delay from the driver's operation, the driver or the passenger may experience the vehicle behavior resulting from the stopping and the re-starting of the internal combustion engine. If the driver or the passenger senses this delay, the driveability of the vehicle is reduced.
Thus, it is preferable to perform a cranking operation for re-starting the internal combustion engine of the vehicle, such as, for example, a gasoline engine or a diesel engine, which has been in a stopped state due to the eco-run control, as quickly as possible. By re-starting the internal combustion engine as quickly as possible, the time taken from establishment of the re-starting condition of the internal combustion engine until the autonomous operation of the internal combustion engine. Generally, a starter, as one type of electric motor, is used for cranking the internal combustion engine. A device disclosed in JP-A-11-122824 includes a main battery and an auxiliary battery that generates a voltage lower than that of the main battery. If the state of charge of the main battery is lower, the auxiliary battery charges the main battery to reliably drive the starter that starts the internal combustion engine.
Conventionally, it is well known that in a hybrid vehicle including an internal combustion engine and an electric motor, the internal combustion engine can be started by the electric motor that drives the vehicle. The electric motor is capable of starting the internal combustion engine faster than the case in which the internal combustion engine is started by the starter. However, the aforementioned control may require an electric motor with a greater capacity, than that of a starter, for starting the internal combustion engine. Therefore, the hybrid vehicle is provided with a high-voltage battery for the electric motor, as the driving source, in addition to an ordinary battery for the starter.
In the above-described device that is disclosed in JP-A-11-122824, the main battery is used as a power source for driving the starter and the auxiliary battery supplies the main battery with electricity only when the state of charge of the main battery is lower. Accordingly, the amount of charge required for driving the starter is kept under the level of electricity supplied from the main battery. Therefore, the time it takes to start the internal combustion engine through manual operation is substantially the same as the time it takes to automatically start the internal combustion engine through the eco-run control. This indicates the difficulty in satisfying the condition of a quick response, which is required for starting-up the internal combustion engine under the eco-run control, even when two types of batteries are employed. The internal combustion engine can always be started quickly by increasing the voltage of the main battery to be higher than that of the battery conventionally employed in the vehicle. However, this may cause the main battery to have an unnecessarily large capacity and thus, deteriorating the durability of the starter.
Further, the electric motor, serving as the driving source, is capable of starting the internal combustion engine of the hybrid vehicle for the driving operation. In this case, the start-up of the internal combustion engine by the electric motor can be performed faster than the start-up of the internal combustion engine by the starter. The aforementioned control for the start-up of the internal combustion engine may require an electric motor with a large capacity that is sufficient for driving the vehicle. Thus, the aforementioned control cannot reasonably be employed in the vehicle other than the hybrid vehicle. In particular, increased capacity of the electric motor, sufficient to run the vehicle, may increase the size of the high-voltage battery, thus increasing the weight of the vehicle body.